Scene complexity and VRAM
I bet those 4x8GB gpus are much faster than single 32GB card. Here are some options:


Get the faster setup and a renderer that can do out-of-core rendering like Octane or Redshift. This allows your GPUs to use system RAM while rendering in exchange of slightly lower render speed. This is something Cycles can't do yet. If you are spending money on hw you might as well get a software.
Get the faster setup and if you hit VRAM limits optimize your scene - you can split the rendering into multiple render layers which you would be probably doing anyway on such large projects.
Getting the 32GB card has also benefits. This comes handy when doing physics simulations accelerated by openCL and you want to fit the ocean or the whole smoke explosion into your card. Blender is not there yet regarding simulations and can't accelerate it on gpu, but if you were using Houdini or something similar you might benefit and need this much VRAM. Simulations can't be easily split like rendering can.


8GB of VRAM is quite a lot and definitely sufficient even for serious production use. Most will be taken by:


~1GB for every 8 million triangles
500MB for Cycles kernel
64MB for each 4k texture (8bit x RGBA)
200MB for each 4k HDR texture (32bit per channel)


When you are not rendering you might want to mine crypto on those gpus and maybe those 4x8GB cards will pay themselves faster than that single 32GB one. Another thing to consider maybe.